Knowledge of the material properties of soft collagenous tissues, such as heart valves, aorta, and ligaments, is fundamental to the understanding of both normal function and disease states. Many studies have reported 1 or 2D material properties; however, there are very few published 3D studies. This lack of data severely hinders development and validation of 3D models. The objective of this proposed research is therefore to (i) develop 3D, anisotropic non-linear viscoelastic models, and (ii) a new experimental/analytical system for measuring 3D load-deformation behavior. 3D finite element models will be created to represent uniaxial, indentation, and shear tests (Specific Aim 1). A hyperelastic version of Fung's quasilinear viscoelasticity theory will be developed. Triaxial stress relaxation and creep tests will be performed using a novel technique for applying combined tension, compression, and shear loads (Specific Aim 2). During loading, high-resolution (appx. 15 pro), multiaxial, 3D video of specimen deformations will be obtained. Using these data, 3D material properties will then be estimated for the different constitutive models via inverse finite element methods with global optimization (Specific Aim 3). These models and data will provide new insights into the constitutive relationships for soft tissue mechanics, and will be of paramount value for the validation of finite element models of biological tissues, and ultimately for bioprosthetic heart valve design. [unreadable] [unreadable] [unreadable]